Carotid endarterectomy is a surgical procedure commonly performed among the elderly to prevent stroke. Its annual incidence is rising rapidly, up 61 percent nationally between 1991 and 1994. Past research has suggested significant quality problems relating to this procedure, including: the selection of inappropriate surgical candidates, high rates of complications in community-based studies, an inverse relationship between provider volume and complications, and substantial racial disparities in use rates. Recent studies have produced much new data on the efficacy of this operation but few new data on quality of care. We propose to investigate quality of care in carotid endarterectomy in a retrospective, multiple cohort, 2-phase study, measuring appropriateness, risk-adjusted complications (death, stroke, and myocardial infarction), and the relationship of specific surgical processes of care to outcomes. In the phase 1, we will study patients treated in a group of 7 collaborating hospitals. In phase 2, we will conduct 2 parallel investigations. We will study a large, stratified random sample of about 8000 Medicare cases from across New York State, a sample large enough to build robust models of risk-adjusted perioperative complications. We will examine appropriateness, risk- adjusted outcomes, and surgical processes of care. Attempting to characterize best surgical practices, we will assess the extent to which specific surgical processes of care are associated with low rates of risk-adjusted perioperative complications. In addition, we will explore the relationship of hospital and surgeon volume to risk-adjusted perioperative complications. We will also assess the relationship between race and appropriateness. In the second part of phase 2, we will design, conduct, and evaluate a series of quality improvement interventions at the 7 collaborating hospitals. With the active participation of the surgeons who perform carotid endarterectomy at these institutions, we will examine the phase 1 data on appropriateness. We will examine differences among collaborating hospitals in the surgical processes of care shown in Phase 2 to be associated with improved risk-adjusted perioperative outcomes. We will determine at each hospital where opportunities exist to improve both the appropriateness of patient selection and the effectiveness of surgical processes of care, intervene to improve, and assess the impact of those interventions.